1. Field of the Invention
The present invention relates to a micromirror actuator, and more particularly to a micromirror actuator with the degrees of freedom of two axes operated by an electrostatic force.
2. Description of the Related Art
Recently, in order to satisfy data transmission requirement in optical communication, wavelength division multiplexing (WDM) networks have been vigorously developed. Thus, since transmission capacity of each wavelength and the number of wavelengths transmitted via a single optical fiber are increased, an optical switch comprising an increased number of pots has been required. Conventional plane waveguides have high optical loss and are large in size. Accordingly, a small-sized micromirror with small optical loss has been developed using a MEMS (Micro-Electro-Mechanical System) technique.
Most of the micromirrors for a three-dimensional optical switch using the MEMS technique are operated by an electrostatic force generated between a reflective surface of the micromirror and an electrode located under the micromirror, and formed in a gimbal structure using an external frame so as to operate two axes in the micromirror. Lucent Technologies Inc. in U.S. discloses the above structure of the micromirror by U.S. patents (U.S. Pat. Nos. 6,300,156 and 6,300,619) in 2001.
Since the micromirror proposed by Lucent Technologies Inc. comprises a sacrificial layer with a small height, the reflective surface of the micromirror should be elevated to a height of several tens of xcexcm by means of an external actuator. Further, since a torsion bar is attached to the micromirror adjacent to the reflective surface, the dimensions of the total structure of the micromirror are larger than that of a portion of the micromirror by which light is actually reflected. Accordingly, it is difficult to densely dispose a plurality of the micromirrors close to each other.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a micromirror actuator, in which a micromirror is elevated to a desired height and the dimensions of its structure are reduced.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a micromirror actuator comprising: a substrate provided with an insulating layer formed thereon; two lower columns spaced from each other by a designated distance, and formed on the insulating layer; a first torsion bar extending over upper surfaces of the lower columns; a second torsion bar formed so that the first and second torsion bars are orthogonal to each other; four electrodes, each disposed in four areas formed by the orthogonal crossing of the first and second torsion bars, formed on the insulating layer; two upper columns formed on an upper surface of the second torsion bar so that upper surfaces of the upper columns are located at higher positions than upper surfaces of the electrodes; and a micromirror located on the upper surfaces of the upper columns so that the micromirror is supported by the upper columns.
Preferably, heights of the electrodes or heights of the upper columns may be varied according to a desired tilted angle of the micromirror.
Further, preferably, the upper surfaces of the electrodes may be rectangular-shaped, quarter circular-shaped, or fan-shaped.
Moreover, preferably, the first and second torsion bars may be straight or curved.